Touchscreen with one carbon nanotube conductive layer

ABSTRACT

The present invention is directed to a touchscreen comprising touch side electrode and device side electrode wherein each electrode comprises an insulating substrate and an exposed electrically conductive layer, wherein said exposed electrically conductive layers are adjacent and separated by dielectric spacers, and wherein only one of the exposed electrically conductive layers comprises carbon nanotubes.

FIELD OF THE INVENTION

The present invention relates in general to touchscreens for electronicdevices. In particular the invention provides a touchscreen comprisingtouch side electrode and device side electrode wherein each electrodecomprises an insulating substrate and an exposed electrically conductivelayer, wherein said exposed electrically conductive layers are adjacentand separated by dielectric spacers, and wherein only one of the exposedelectrically conductive layers comprises carbon nanotubes.

BACKGROUND OF THE INVENTION

Devices such as flat-panel displays typically contain a substrateprovided with an indium tin oxide (ITO) layer as a transparentelectrode. The coating of ITO is carried out by vacuum sputteringmethods, which involve high substrate temperature conditions up to 250°C., and therefore, glass substrates are generally used. The high cost ofthe fabrication methods and the low flexibility of such electrodes, dueto the brittleness of the inorganic ITO layer as well as the glasssubstrate, limit the range of potential applications. As a result, thereis a growing interest in making all-organic devices, comprising plasticresins as a flexible substrate and carbon nanotube or organicelectroconductive polymer layers as an electrode. Such plasticelectronics allow low cost devices with new properties. Flexible plasticsubstrates can be provided with an electroconductive polymer layer bycontinuous hopper or roller coating methods (compared to batch processsuch as sputtering) and the resulting organic electrodes enable the“roll to roll” fabrication of electronic devices which are moreflexible, lower cost, and lower weight. Touchscreens (also referred toas touch panels or touch switches) are widely used in conventional CRTsand in flat-panel display devices in computers and in particular withportable computers. FIG. 1 shows a typical prior art resistive-typetouchscreen 10 comprising a first electrode 15 that is on the side ofthe touchscreen that is nearer to the device that is referred hereinbelow as the device side electrode and a second electrode 16 that is onthe side of the touchscreen that is nearer to the user that is referredherein below as the touch side electrode. Device side electrode 15comprises a transparent substrate 12, having a first conductive layer14. Touch side electrode 16 comprises a transparent support 17, that istypically a flexible transparent support, and a second conductive layer18 that is physically separated from the first conductive layer 14 bydielectric (insulating) spacer elements 20. A voltage is developedacross the conductive layers. The conductive layers 14 and 18 have aresistance selected to optimize power usage and position sensingaccuracy. Deformation of the touch side electrode 16 by an externalobject such as a finger or stylus causes the second conductive layer 18to make electrical contact with first conductive layer 14, therebytransferring a voltage between the conductive layers. The magnitude ofthis voltage is measured through connectors (not shown) connected tometal bus bar conductive patterns (not shown) formed on the edges ofconductive layers 18 and 14 to locate the position of the deformingobject.

ITO is commonly employed as the transparent conductive layer on thedevice side and touch side electrodes. However, ITO tends to crack understress and with the result that the conductivity of the electrodes,especially for the touch side electrode, is diminished and theperformance of the touchscreen degraded. More flexible conductivepolymer-containing layers have also been considered for thisapplication, but these conductive polymers are softer and lessphysically durable than ITO and therefore such conductive layers tend todegrade after repeated contacts.

Single wall carbon nanotubes (SWCNTs) are essentially graphene sheetsrolled into hollow cylinders thereby resulting in tubules composed ofsp2 hybridized carbon arranged in hexagons and pentagons, which haveouter diameters between 0.4 nm and 10 nm. These SWCNTs are typicallycapped on each end with a hemispherical fullerene (buckyball)appropriately sized for the diameter of the SWCNT. However, these endcaps may be removed via appropriate processing techniques leavinguncapped tubules. SWCNTs can exist as single tubules or in aggregatedform typically referred to as ropes or bundles. These ropes or bundlesmay contain several or a few hundred SWCNTs aggregated through Van derWaals interactions forming triangular lattices where the tube-tubeseparation is approximately 3-4 Å. Ropes of SWCNTs may be composed ofassociated bundles of SWCNTs.

The inherent properties of SWCNTs make them attractive for use in manyapplications. SWCNTs can possess high (e.g. metallic conductivities)electronic conductivities, high thermal conductivities, high modulus andtensile strength, high aspect ratio and other unique properties.Further, SWCNTs may be metallic, semi-metallic, or semiconductingdependant on the geometrical arrangement of the carbon atoms and thephysical dimensions of the SWCNT. To specify the size and conformationof single-wall carbon nanotubes, a system has been developed, describedbelow, and is currently utilized. SWCNTs are described by an index (n,m), where n and m are integers that describe how to cut a single stripof hexagonal graphite such that its edges join seamlessly when the stripis wrapped into the form of a cylinder. When n=m e.g. (n, n), theresultant tube is said to be of the “arm-chair” or (n, n) type, sincewhen the tube is cut perpendicularly to the tube axis, only the sides ofthe hexagons are exposed and their pattern around the periphery of thetube edge resembles the arm and seat of an arm chair repeated n times.When m=0, the resultant tube is said to be of the “zig zag” or (n,0)type, since when the tube is cut perpendicular to the tube axis, theedge is a zig zag pattern. Where n≠m and m≠0, the resulting tube haschirality. The electronic properties are dependent on the conformation;for example, armchair tubes are metallic and have extremely highelectrical conductivity. Other tube types are semimetals orsemi-conductors, depending on their conformation. SWCNTs have extremelyhigh thermal conductivity and tensile strength irrespective of thechirality. The work functions of the metallic (approximately 4.7 eV) andsemiconducting (approximately 5.1 eV) types of SWCNTs are different.

Similar to other forms of carbon allotropes (e.g. graphite, diamond)these SWCNTs are intractable and essentially insoluble in most solvents(organic and aqueous alike). Thus, SWCNTs have been extremely difficultto process for various uses. Several methods to make SWCNTs soluble invarious solvents have been employed. One approach is to covalentlyfunctionalize the ends of the SWCNTs with either hydrophilic orhydrophobic moieties. A second approach is to add high levels ofsurfactant and/or dispersants (small molecule or polymeric) to helpsolubilize the SWCNTs.

Lavin et al. in U.S. Pat. No. 6,426,134 disclose a method to formpolymer composites using SWCNTs. This method provides a means to meltextrude a SWCNT/polymer composite wherein at least one end of the SWCNTis chemically bonded to the polymer, where the polymer is selected froma linear or branched polyamide, polyester, polyimide, or polyurethane.This method does not provide opportunities for solvent based processingand is limited to melt extrusion which can limit opportunities forpatterning or device making. The chemically bonded polymers identifiedtypically have high molecular weights and could interfere with somematerial properties of the SWCNTs (e.g. electronic or thermal transport)via wrapping around the SWCNTs and preventing tube-tube contacts.

Connell et al in U.S. Patent Application Publication 2003/0158323 A1describes a method to produce polymer/SWCNT composites that areelectronically conductive and transparent. The polymers (polyimides,copolyimides, polyamide acid, polyaryleneether, polymethylmethacrylate)and the SWCNTs or MWCNTs are mixed in organic solvents (DMF,N,N-dimethlacetamide, N-methyl-2-pyrrolidinone, toluene) to cast filmsthat have conductivities in the range of 10⁻⁵-10⁻¹² S/cm with varyingtransmissions in the visible spectrum. Additionally, monomers of theresultant polymers may be mixed with SWCNTs in appropriate solvents andpolymerized in the presence of these SWCNTs to result in composites withvarying weight ratios. The conductivities achieved in these polymercomposites are several orders of magnitude too low and not optimal foruse in most electronic devices as electronic conductors or EMI shields.Additionally, the organic solvents used are toxic, costly and poseproblems in processing. Moreover, the polymers used or polymerized arenot conductive and can impede tube-tube contact further increasing theresistivity of the composite.

Kuper et al in Publication WO 03/060941A2 disclose compositions to makesuspended carbon nanotubes. The compositions are composed of liquids andSWCNTs or MWCNTs with suitable surfactants (cetyl trimethylammoniumbromide/chloride/iodide). The ratio by weight of surfactant to SWCNTsgiven in the examples range from 1.4-5.2. This method is problematic, asit needs extremely large levels of surfactant to solubilize the SWCNTs.The surfactant is insulating and impedes conductivity of a filmdeposited from this composition. The surfactant may be washed from thefilm but this step adds complexity and may decrease efficiency inprocessing. Further, due to the structure formed in films deposited fromsuch a composition, it would be very difficult to remove all thesurfactant.

Papadaopoulos et al. in U.S. Pat. No. 5,576,162 describe an imagingelement, which comprises carbon nanofibers to be used primarily as ananti-static material within the imaging element. These materials may notprovide the highly transparent and highly conductive (low sheetresistance, R_(S)) layer that is necessary in many current electronicdevices, especially displays.

Smalley et al in U.S. Pat. No. 6,645,455 disclose methods to chemicallyderivatize SWCNTs to facilitate solvation in various solvents. Primarilythe various derivative groups (alkyl chains, acyl, thiols, aminos, arylsetc.) are added to the ends of the SWCNTs. The side-walls of the SWCNTsare functionalized primarily with fluorine groups resulting influorinated SWCNTs. The solubility limit of such “fluorotubes” in2-propanol is approximately 0.1 mg/mL and in water or water/acetonemixtures the solubility is essentially zero. The fluorinated SWCNTs weresubjected to further chemical reactions to yield methylated SWCNTs andthese tubes have a low solubility in Chloroform but not other solvents.Such low concentrations are impractical and unusable for most depositiontechniques useful in high quantity manufacturing. Further, such highliquid loads need extra drying considerations and can destroy patternedimages due to intermixing from the excess solvent. In addition, themethod discloses functionalization of the tubule ends with variousfunctionalization groups (acyl, aryl, aralkyl, halogen, alkyl, amino,halogen, thiol) but the end functionalization alone may not be enough toproduce viable dispersions via solubilization. Further, the sidewallfunctionalization is done with fluorine only, which gives limitedsolubility in alcohols, which can make manufacturing and productfabrication more difficult. Additionally, the fluorinated SWCNTs areinsulators due to the fluorination and thereby are not useful forelectronic devices especially as electronic conductors. Moreover, thechemical transformations needed to add these functional groups to theend points of the SWCNTs require additional processing steps andchemicals which can be hazardous and costly.

Smalley et al. in U.S. Pat. No. 6,683,783 disclose methods to purifySWCNT materials resulting in SWCNTs with lengths from 5-500 nm. Withinthis patent, formulations are disclosed that use 0.5 wt % of asurfactant, Triton X-100 to disperse 0.1 mg/mL of SWCNT in water. Suchlow concentrations are impractical and unusable for most depositiontechniques useful in high quantity manufacturing. Further, such highliquid loads need extra drying considerations and can destroy patternedimages due to intermixing from the excess solvent. In addition, themethod discloses functionalization of the tubule ends with variousfunctionalization groups (acyl, aryl, aralkyl, halogen, alkyl, amino,halogen, thiol) but the end functionalization alone may not be enough toproduce viable dispersions via solubilization. Moreover, the chemicaltransformations needed to add these functional groups to the end pointsof the SWCNTs require additional processing steps and chemicals whichcan be hazardous and costly. Also, the patent discloses a composition ofmatter, which is at least 99% by weight of single wall carbon moleculeswhich obviously limits the amount of functionalization that can be putonto the SWCNTs thereby limiting its solubilization levels andprocessability.

Rinzler et al. in PCT Publication WO2004/009884 A1 disclose a method offorming SWCNT films on a porous membrane such that it achieves 200ohms/square and at least 30% transmission at a wavelength of 3 um. Thismethod is disadvantaged since it needs a porous membrane (e.g.polycarbonate or mixed cellulose ester) with a high volume of porositywith a plurality of sub-micron pores as a substrate which may lose asignificant amount of the SWCNT dispersion through said pores therebywasting a significant amount of material. Also, such membranes may nothave the optical transparency required for many electronic devices suchas displays. Further, the membrane is set within a vacuum filtrationsystem, which severely limits the processability of such a system andmakes the roll-to-roll coating application of the SWCNT solutionimpossible. Moreover, the weight percent of the dispersion used to makethe SWCNT film was 0.005 mg/mL in an aqueous solution. Such weightpercents are impractical and unusable in most coating and depositionsystems with such a high liquid load. Such high liquid loads make itvirtually impossible to make patterned images due to solvent spreadingand therefore image bleeding/destruction.

Blanchet-Fincher et al in Publication WO 02/080195A1 and in US20040065970 A1 illustrate high conductivity compositions composed ofpolyaniline (PANI) and SWCNTs or MWCNTs and methods to deposit suchcompositions from a donor element onto a receiver substrate. Thenitrogen base salt derivative of emeraldine polyaniline is mixed withSWCNTs in organic solvents (toluene, xylene, turpinol, aromatics) andcast into films with conductivity values of 62 S/cm (1 wt % SWCNT inPANI) and 44 S/cm (2 wt % SWCNT in PANI). These films alternatively maybe produced as part of a multi-layer donor structure suitable as use fora material transfer system. The PANI/SWCNT composite are transferredfrom the donor sheet to a suitable receiver substrate in imagewise form.PANI is a highly colored conductive polymer and may result in aconductive composite with unsatisfactory transparency and color, whichmay be undesirable for applications such as displays.

Hsu in WO 2004/029176 A1 disclose compositions for electronicallyconducting organic polymer/nanoparticle composites. Polyaniline(Ormecon) or PEDT (Baytron P) are mixed with Molybdenum nanowires orcarbon nanotubes (8 nm diameter, 20 um length, 60 S/cm). Thecompositions disclosed in this invention are disadvantaged by marginalconductivity.

Arthur et al in PCT Publication WO 03/099709 A2 disclose methods forpatterning carbon nanotubes coatings. Dilute dispersions (10 to 100 ppm)of SWCNTs in isopropyl alcohol (IPA) and water (which may includeviscosity modifying agents) are spray coated onto substrates. Afterapplication of the SWCNT coating, a binder is printed in imagewisefashion and cured. Alternatively, a photo-definable binder may be usedto create the image using standard photolithographic processes.Materials not held to the substrate with binder are removed by washing.Dilute dispersions (10 to 100 ppm) of SWCNTs in isopropyl alcohol (IPA)and water with viscosity modifying agents are gravure coated ontosubstrates. Dilute dispersions (10 to 100 ppm) of SWCNTs in isopropylalcohol (IPA) and water are spray coated onto substrates. The coatedfilms are then exposed through a mask to a high intensity light sourcein order to significantly alter the electronic properties of the SWCNTs.A binder coating follows this step. The dispersion concentrations usedin these methods make it very difficult to produce images via directdeposition (inkjet etc.) techniques. Further, such high solvent loadsdue to the low solids dispersions create long process times anddifficulties handling the excess solvent. In addition, these patterningmethods are subtractive processes, which unnecessarily waste the SWCNTmaterial via additional removal steps thereby incurring cost and processtime. This application also discloses method to make conductivecompositions and coatings from such compositions but it does not teachsatisfactory methods nor compositions to execute such methods.

Transparent electronically-conductive layers (TCL) of metal oxides suchas indium tin oxide (ITO), antimony doped tin oxide, and cadmiumstannate (cadmium tin oxide) have been used in the manufacture ofelectrooptical display devices such as liquid crystal display devices(LCDs), electroluminescent display devices, photocells, touchscreens,solid-state image sensors and electrochromic windows or as components ofthese devices such as electromagnetic interference (EMI) shielding.

Intrinsically conductive (also referred to as electronically conductive)polymers have recently received significant attention from variousindustries because of their electronic conductivity. Although many ofthese polymers are highly colored and are less suited for TCLapplications, some of these intrinsically conductive polymers, such assubstituted or unsubstituted pyrrole-containing polymers (as mentionedin U.S. Pat. Nos. 5,665,498 and 5,674,654), substituted or unsubstitutedthiophene-containing polymers (as mentioned in U.S. Pat. Nos. 5,300,575,5,312,681, 5,354,613, 5,370,981, 5,372,924, 5,391,472, 5,403,467,5,443,944, 5,575,898, 4,987,042, and 4,731,408) and substituted orunsubstituted aniline-containing polymers (as mentioned in U.S. Pat.Nos. 5,716,550, 5,093,439, and 4,070,189) are transparent and notprohibitively colored, at least when coated in thin layers at moderatecoverage. Because of their electronic conductivity instead of ionicconductivity, these polymers are conducting even at low humidity.

The application of electronically conductive polymers in display relateddevice has been envisioned in the past. European Patent ApplicationEP9910201 describes a light transmissive substrate having a lighttransmissive conductive polymer coating for use in resistivetouchscreens. U.S. Pat. No. 5,738,934 describes touchscreen cover sheetshaving a conductive polymer coating.

Use of commercial polythiophene coated sheet such as Orgacon from Agfahas been suggested for manufacturing of thin film inorganiclight-emitting diode has been suggested in U.S. Pat. No. 6,737,293.However, as discussed later, the transparency vs. surface electricalresistivity of such products may not be sufficient for someapplications.

Use of conductive high molecular film for preventing the fringe field inthe in-plane switching mode in liquid crystal display has been proposedin U.S. Pat. No. 5,959,708. However, the conductivity requirement forthese films appears to be not very stringent. For example, in oneembodiment (col. 5, lines 6-10) the high molecular film can be totallynon-conductive. Moreover, U.S. Pat. No. 5,959,708 does not refer to anyspecification involving transmission characteristics of these films.

Use of transparent coating on glass substrates for cathode ray tubesusing polythiophene and silicon oxide composites has been disclosed inU.S. Pat. No. 6,404,120. However, the method suggests in-situpolymerization of an ethylenedioxythiohene monomer on glass, baking itat an elevated temperature and subsequent washing with tetra ethylorthosilicate. Such an involved process may be difficult to practice forroll-to-roll production of a wide flexible plastic substrate.

Use of in-situ polymerized polythiophene and polypyrrole has beenproposed in U.S. Pat Appl. Pub. 2003/0008135 A1 as conductive films, forITO replacement. As mentioned earlier, such processes are difficult toimplement for roll-to-roll production of conductive coatings. In thesame patent application, a comparative example was created using adispersion of poly (3,4 ethylene dioxythiophene)/polystyrene sulfonicacid which resulted in inferior coating properties.

Addition of conductivity enhancing agents such as organic compounds withdihydroxy or polyhydroxy and/or carboxyl groups or amide groups orlactam groups is suggested for incorporation in polythiophene in U.S.Pat. No. 5,766,515.

As indicated herein above, the art discloses a wide variety ofelectronically conductive TCL compositions that can be incorporated inelectronic devices. However, the stringent requirements of hightransparency, low surface electrical resistivity, flexibility, androbustness under repeated contacts demanded by modern display devicesand, especially, touchscreens is extremely difficult to attain with theTCL compositions described in the prior art. Thus, there is still acritical need for transparent conductors that can be coated roll-to-rollon a wide variety of substrates under typical manufacturing conditionsusing environmentally desirable components. In addition to providingsuperior touchscreen electrode performance, the TCL layers also must behighly transparent, must resist the effects of humidity change, bephysically robust, and be manufacturable at a reasonable cost.

PROBLEM TO BE SOLVED BY THE INVENTION

There is a need to provide improved touchscreen electrodes, preferablyobtained by wet coating, roll-to-roll manufacturing methods, that moreeffectively meet the demanding requirements of touchscreens than thoseof the prior art.

SUMMARY OF THE INVENTION

The present invention provides a touchscreen comprising touch sideelectrode and device side electrode wherein each electrode comprises aninsulating substrate and an exposed electrically conductive layer,wherein said exposed electrically conductive layers are adjacent andseparated by dielectric spacers, and wherein only one of the exposedelectrically conductive layers comprises carbon nanotubes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. A schematic diagram showing a section of a resistive touchscreenof the prior art.

FIG. 2. A schematic diagram showing a section of a resistive touchscreenemploying asymmetric electrodes of the present invention.

FIG. 3. Shows another embodiment of a resistive-type touchscreen of theinvention.

FIG. 4. Shows another embodiment of a resistive-type touchscreen of theinvention.

FIG. 5. An exploded view showing the construction of a touchscreen ofthe present invention.

FIGS. 6A and 6B. Schematic diagrams of pristine single wall carbonnanotubes having tubules with closed ends and with open ends.

FIGS. 7A and 7B. Schematic diagrams of functionalized single wall carbonnanotubes having tubules with closed ends and with open ends

FIG. 8. An exploded view showing the touchscreen fabricated in thisinvention for testing of single and multilayer electrodes of the instantinvention.

FIG. 9. Shows, based on the results of Comparative Example 1 below, theon-state resistance profile as a function of single point actuations fora single layer Bekaert ITO touch switch.

FIG. 10. Shows, based on the results of Comparative Example 1 below, theforce to actuate the touchswitch as a function of single pointactuations for single layer of Bekaert ITO.

FIG. 11. Shows, based on the results of Comparative Example 2 below, theforce to actuate the touchswitch as a function of single pointactuations for single layer of Baytron P AG (PEDOT/PSS).

FIG. 12. Shows, based on the results of Comparative Example 2 below, theon-state resistance profile as a function of single point actuations forsingle layer conductor Baytron P AG Touch Switch.

FIG. 13. Shows, based on the results of Comparative Example 4 below, theforce to actuate the touchswitch as a function of single pointactuations for single layer conductor Keytec ITO Touch Switch.

FIG. 14. Shows, based on the results of Comparative Example 4 below, theon-state resistance profile as a function of single point actuations forsingle layer conductor Keytec ITO Touch Switch.

FIG. 15. Shows, based on the results of Comparative Example 5 below, theon-state resistance profile as a function of single point actuations foran asymmetric electrode touch switch with Keytec ITO and Baytron P AG asopposing electrodes.

FIG. 16. Shows, based on the results of Instant Invention Example 1below, the force to actuate the touchswitch as a function of singlepoint actuations for an asymmetric electrode touch switch with BekaertITO and Single Wall Carbon Nanotubes as per the instant invention.

FIG. 17. Shows, based on the results of Instant Invention Example 1below, the on-state resistance profile as a function of single pointactuations for an asymmetric electrode touch switch with Bekaert ITO andSingle Wall Carbon Nanotubes as per the instant invention.

FIG. 18. Shows, based on the results of Instant Invention Example 2below, the force to actuate the touchswitch as a function of singlepoint actuations for an asymmetric electrode touch switch with Baytron PAG (containing crosslinking agent) and Single Wall Carbon Nanotubes asper the instant invention.

FIG. 19. Shows, based on the results of Instant Invention Example 2below, the on-state resistance profile as a function of single pointactuations for an asymmetric electrode touch switch with Baytron P AG(containing crosslinking agent) and Single Wall Carbon Nanotubes as perthe instant invention.

FIG. 20. Shows, based on the results of Instant Invention Example 3below, the force to actuate the touchswitch as a function of singlepoint actuations for an asymmetric electrode touchswitch with Keytec ITOand Carbon Nanotube (exposed layer) and Pedot/PSS (first or buriedlayer) as Opposing Electrodes.

FIG. 21. Shows, based on the results of Instant Invention Example 3below, the on-state resistance profile as a function of single pointactuations for an asymmetric electrode touchswitch with Keytec ITO andCarbon Nanotube (exposed layer) and Pedot/PSS (first or buried layer) asOpposing Electrodes.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a touchscreen comprising touch sideelectrode and device side electrode wherein each electrode comprises aninsulating substrate and an exposed electrically conductive layer,wherein said exposed electrically conductive layers are adjacent andseparated by dielectric spacers, and wherein only one of the exposedelectrically conductive layers comprises carbon nanotubes.

Touchscreens of the present invention comprise electrodes that areasymmetric in composition. That is, a different conductive material isemployed in the exposed electrically conductive layer on the touch sideelectrode compared to the exposed electrically conductive layer on thedevice side electrode. In the present invention, either the touch sideelectrode or the device side electrode (but not both) has an exposedelectrically conductive layer that comprises carbon nanotubes.Additionally, electrodes that are on opposite sides of the spacerelements may also be called opposing electrodes. Such opposingelectrodes of the present invention comprise electrodes that areasymmetric in composition.

Touchscreens of the present invention, wherein only one of the exposedconductive layers comprise carbon nanotubes, provide improved durabilityof the touchscreen compared with conventional touchscreens employing(symmetrical composition) touch side and device side electrodescomprising ITO. These and other advantages will be apparent from thedetailed description below.

FIG. 2 shows one embodiment of a resistive-type touchscreen of theinvention 39 including a device side electrode 25 and a touch sideelectrode 26. Device side electrode 25 comprises in order, an insulatingsubstrate 29 and an exposed electrically conductive layer 24 in contactwith said substrate. Touch side electrode 26 comprises in order, aninsulating substrate 27 and an exposed electrically conductive layer 28in contact with said substrate. Wherein said exposed electricallyconductive layers 24 and 28 are adjacent and separated by dielectricspacers 32. Preferably, the exposed electrically conductive layers havea sheet resistance of between 100 and 10⁶ Ohm per square.

In the embodiment depicted in FIG. 2, either exposed electricallyconductive layer 24 or 28 (but not both) comprises carbon nanotubes.Preferably, the carbon nanotubes are single wall carbon nanotubes(SWCNT). The other exposed electrically conductive layer that does notcomprise carbon nanotubes may comprise at least one material from thegroup consisting of electronically conductive polymers, transparentconducting oxides and transparent metal films. Suitable electronicallyconductive polymers include polypyrrole, polyaniline or polythiophene.Suitable transparent conducting oxides include tin doped indium oxide,fluorine doped zinc oxide, aluminum doped zinc oxide, indium doped zincoxide, antimony doped tin oxide, fluorine doped tin oxide. Suitabletransparent metal films include silver, gold, copper or alloys of thesematerials.

Resistive touchscreens of the invention preferably are mechanicallyrobust to point actuations by objects (plastic or metal stylus, fingersetc.). A touchscreen is activated or actuated when the touch side anddevice side electrodes contact. Over time, repetitive contact and theforce applied during such contact damage prior art touchscreens. Suchdamage requires that increasingly larger forces are necessary to actuatethe touchscreen. In a preferred embodiment of the instant invention, theforce required to actuate a point on the touchscreen does not change bymore than 500 percent over 500,000 single point actuations. Morepreferably, the force required to actuate the touchscreen does notchange by more than 100 percent and most preferably more than 50percent. A single point actuation is the application of an object at asingle point on the touchscreen to activate such touchscreen.

The carbon nanotubes suitable for use in the conductive layers of theinvention may be formed by any known methods in the art (laser ablation,CVD, arc discharge). The carbon nanotubes are preferred to have minimalor no impurities of carbonaceous impurities that are not carbonnanotubes (graphite, amorphous, diamond, non-tubular fullerenes,multiwall carbon nanotubes) or metal impurities. It is found that thetransparency increases significantly with reduced levels of metallic andcarbonaceous impurities. Conductive layer film quality, as evidenced bylayer uniformity, surface roughness, and a reduction in particulates,also improves with a decrease in the amount of metal and carbonaceousimpurities.

To achieve high electronic conductivity, metallic SWCNTs are the mostpreferred type of carbon nanotube but semimetallic and semiconductingSWCNTs may also be used. A pristine SWCNT means that the surface of theSWCNT is free of covalently functionalized materials either throughsynthetic prep, acid cleanup of impurities, annealing or directedfunctionalization. For the purpose of the present invention, however,the SWCNTS are preferably functionalized. The preferred functional groupis a hydrophilic species selected from carboxylic acid, carboxylateanion (carboxylic acid salt), hydroxyl, sulfur containing groups,carbonyl, phosphates, nitrates or combinations of these hydrophilicspecies. In some applications other types of functionalization such aspolymer, small molecule or combinations thereof may be required. Forexample, such functionalization may improve the compatibility of theSWCNT in a particular polymer matrix.

Turning now to FIG. 5, pristine SWCNTs with either open or closed endsare illustrated. SWCNTs that are pristine are essentially intractable inmost solvents, especially aqueous media, without the use of high levelsof dispersants. Therefore, it is not possible to use only pristineSWCNTs and water to produce an aqueous coating composition. FIG. 6exemplifies the basic structure of covalently functionalized SWCNTs. TheX in FIG. 6 may be selected from one of the hydrophilic species listedabove. It is worth noting that the X may be positioned at any point onthe SWCNT, external or internal surface, open or closed end, orsidewall. It is preferred that the X be uniformly distributed across theexternal surface, potentially for the most effectiveness.

The most preferred covalent surface functionalization is carboxylic acidor a carboxylic acid salt or mixtures thereof (hereafter referred to asonly carboxylic acid). For carboxylic acid based functionalization, thepreferred level of functionalized carbons on the SWCNT is 0.5-100 atomicpercent, where 1 atomic percent functionalized carbons would be 1 out ofevery 100 carbons in the SWCNT have a functional group covalentlyattached. The functionalized carbons may exist anywhere on the nanotubes(open or closed ends, external and internal sidewalls). As alreadymentioned, preferably the functionalization is on the external surfaceof the SWCNTs. More preferably the functionalized percent range is0.5-50 atomic percent, and most preferably 0.5-5 atomic percent.Functionalization of the SWCNTs with these groups within these atomicpercent ranges allows the preparation of stable dispersions at thesolids loadings necessary to form highly conductive, transparent filmsby conventional coating means. This method allows for very effectivedispersion in substantially aqueous dispersions and does not require adispersion aid. Additionally, the most efficient level offunctionalization will provide the desired dispersion withoutsignificantly altering the electronic properties of the carbonnanotubes. Transparency is defined as a conductive layer that hasgreater than 60% bulk transmission. This transparency may be achieved byproducing thin coatings with thicknesses less than 1 micrometer. Thefunctionalization may be carried out by a number of routes. Typically,the raw material (unfunctionalized) SWCNTs are added to a bath ofstrongly oxidizing agents (hydrochloric acid, hydrofluoric acid,hydrobromic acid, hydroiodic acid, sulfuric acid, oleum, nitric acid,citric acid, oxalic acid, chlorosulfonic acid, phosphoric acid,trifluoromethane sulfonic acid, glacial acetic acid, monobasic organicacids, dibasic organic acids, potassium permanganate, persulfate,cerate, bromate, hydrogen peroxide, dichromate) which may be mixtures.Sulfuric acid, nitric acid, permanganate, and chlorosulfonic acids arepreferred due to the efficacy of the oxidation and functionalization.Temperatures from 20° C.-120° C. are typically used in reflux of thismixture of SWCNTs and strong oxidizing agents with appropriate agitationover 1 hr-several days process time. At the end of this process, the rawSWCNTs are now functionalized SWCNTs. The residual oxidizing agents areremoved via separation technologies (filtration wash, centrifugation,cross-flow filtration) such that a powder of the functionalized SWCNTs(primarily carboxylic acid functionalities) remains after appropriateheating to dry.

The pH of the dispersion and the coating composition is important. Asthe pH becomes more basic (above the pKa of the carboxylic acid groups),the carboxylic acid will be ionized thereby making the carboxylateanion, a bulky, repulsive group which can aid in the stability.Preferred pH ranges from 3-10 pH. More preferred pH ranges from 3-6.

The length of the SWCNTs may be from 20 nm-1 m, more typically from 20nm to 50 um. The SWCNTs may exist as individual SWCNTs or as bundles ofSWCNTs. The diameter of a SWCNT in the conductive layer may be 0.05 nm-5nm. The SWCNTs in bundled form may have diameters ranging from 1 nm-1um. Preferably such bundles will have diameters less than 50 nm andpreferably less than 20 nm and lengths of between 20 nm and 50 um. It isimportant that higher surface area is achieved to facilitate transfer ofelectrons and higher available surface area is achieved by havingsmaller bundle sizes thereby exposing surfaces of SWCNTs which may be atthe internal position of the bundles and not accessible. The ends of theSWCNTs may be closed by a hemispherical buckyball of appropriate size.Alternatively, both of the ends of the SWCNTs may be open. Some casesmay find one end open and the other end closed.

The functionalized SWCNTs (produced as described above or purchased froma vendor) are used to form aqueous dispersions with SWCNT solidsloadings in the 0.05-10 wt % (500-100000) ppm range. More preferably theSWCNT solids loadings are 0.1-5 wt %. Most preferably the solid loadingsare 0.1-1 wt % SWCNT. This solids loading range allows for facilecoating to occur and also minimizes the viscosity such that roll coatingand/or inkjet printing can be performed in standard practice. Thefunctionalized SWCNTs are often in powder/flake form and require energyto disperse. A typical dispersion process may use a high shear mixingapparatus (homogenizer, microfluidizer, cowles blade high shear mixer,automated media mill, ball mill) for several minutes to an hour. We havealso found that standard ultrasonication and bath sonication may besufficient to disperse the functionalized SWCNTs. Typically, a 1000 ppmSWCNT dispersion in deionized water is formed by bath sonication for2-24 hrs (dependant on the level of hydrophilic functionalization).After the dispersion process, pH can be adjusted to desired range. Acentrifugation or filtration process is used to remove largeparticulates. The resultant dispersion will be stable for several monthson standing (dependant on the level of hydrophilic functionalization).This dispersion has solids loadings high enough to produce conductivecoatings in single pass modes for many coating techniques.

The conductive layer of the invention should contain about 0.1 to about1000 mg/m² dry coating weight of the functionalized SWCNT. Preferably,the conductive layer should contain about 0.5 to about 500 mg/m² drycoating weight of the functionalized SWCNT. This range of SWCNT in thedry coating is easily accessible by standard coating methods, will givethe best transmission properties, and minimizes cost to achieve thedesired sheet resistance. The actual dry coating weight of the SWCNTsapplied is determined by the properties for the particular conductivefunctionalized SWCNT employed and by the requirements for the particularapplication, the requirements may include, for example, theconductivity, transparency, optical density, cost, etc for the layer.

In a preferred embodiment, the layer containing the conductive SWCNTs isprepared by applying a mixture containing:

a) a SWCNT according to Formula I;

wherein each of R¹ and R² independently represents carboxylic acid,carboxylate anion (carboxylic acid salt), hydroxyl, sulfur containinggroups, carbonyl, phosphates, nitrates, and the tube is a single wallcarbon nanotube composed of carbon atoms substantially in hexagonalconfiguration, and, optionally

b) a dispersant and, optionally

c) a polymeric binder.

The R¹ and R² substituents may be uniformly or non-uniformly distributedacross the SWCNT. The dispersant loading in the dispersion is preferredto be minimal to none. The maximum dispersant loading is preferred to be50 wt % of the weight of the SWCNT. The more preferred dispersantloading is less than 5 wt % of the weight of the SWCNT. The mostpreferred dispersant loading is 0 wt %. With decreasing levels ofdispersant, the electronic conductivity increases. There are manydispersants which may be chosen. Preferred dispersants are octylphenolethoxylate (TX-100), sodium dodecyl sulfate, sodiumdodecylbenzenesulfonate, poly(styrene sulfonate), sodium salt,poly(vinylpyrrolidone), block copolymers of ethylene oxide and propyleneoxide (Pluronics or Poloxamers), Polyoxyethylene alkyl ethers (Brij 78,Brij 700), and cetyl or dodecyltrimethylammonium bromide. Thesedispersants are able to effectively disperse carbon nanotubes at lowdispersant loadings which is preferred so that the impact on electronicconductivity is minimal. Appropriate mixtures of these dispersants maybe utilized.

Additionally, a preferred embodiment for functionalization of thisinvention can preferably be where the functional group is a sulfurcontaining group selected from:R—SO_(x)Z_(y)Where R is a carbon within the lattice of a SWCNT, x may range from 1-3and Z may be a Hydrogen atom or a metal cation such metals as Na, Mg, K,Ca, Zn, Mn, Ag, Au, Pd, Pt, Fe, Co and y may range from 0-1 orcombinations these hydrophilic species. The sulfur containing groupslisted above may be sulfonic acid, sulfonic acid and/or sulfonic acidand/or the corresponding anions or mixtures thereof. The most preferredsulfur containing group covalent surface functionalization is sulfonicacid or a sulfonic acid salt or mixtures thereof (hereafter referred toas only sulfonic acid). Covalently attached sulfonic acid gives bestdispersions of carbon nanotubes amongst the sulfur containing groups.

For environmental reasons, substantially aqueous dispersions of carbonnanotubes (meaning at least 60 wt % water in the dispersion) arepreferred for application of the carbon nanotube layer.

Electronically conductive polymers that are suitable in the practice ofthe invention may be soluble or dispersible in organic solvents or wateror mixtures thereof. The conductive poly(3,4-ethylenedioxythiophene)(PEDOT) may be supplied by either of two routes. First, it may besynthesized via an in-situ oxidative polymerization where the monomer,ethylenedioxythiophene (EDOT), is dissolved within a suitable solvent(e.g. butanol). There are a number of oxidizing agents that may be usedincluding ammonium persulfate, and iron(III) salts of organic andinorganic acids. Second, an aqueous dispersion of a cationic PEDOT mixedwith a polyanion, such as polystyrenesulfonic acid, may be used. Forenvironmental reasons, aqueous compositions are preferred.

A preferred electronically conductive polymer comprises 3,4-dialkoxysubstituted polythiophene styrene sulfonate because of its relativelyneutral color. The most preferred electronically conductive polymersinclude poly(3,4-ethylene dioxythiophene styrene sulfonate) whichcomprises poly(3,4-ethylene dioxythiophene) in a cationic form withpolystyrenesulfonic acid. The advantage of choosing the aforementionedpolymers arise from the fact that they are primarily water based, stablepolymer structure to light and heat, stable dispersions and causeminimum concern for storage, health, environmental and handling. Thepolystyrenesulfonic acid is preferred as it stabilizes the PEDOT polymervery efficiently and helps in dispersion in aqueous systems. Analternative electronically conductive polymer is polyaniline.

The conductive poly(3,4-ethylenedioxythiophene) (PEDOT) may be suppliedby either of two routes. First, it may be synthesized via an in-situoxidative polymerization where the monomer, ethylenedioxythiophene(EDOT), is dissolved within a suitable solvent (e.g. butanol). There area number of oxidizing agents that may be used including ammoniumpersulfate, and iron(III) salts of organic and inorganic acids. Second,an aqueous dispersion of a cationic PEDOT mixed with a polyanion, suchas polystyrenesulfonic acid, may be used. For environmental reasons,aqueous compositions are preferred.

Preparation of the aforementioned polythiophene-based polymers has beendiscussed in detail in a publication titled“Poly(3,4-ethylenedioxythiophene) and its derivatives: past, present andfuture” by L. B. Groenendaal, F. Jonas, D. Freitag, H. Pielartzik and J.R. Reynolds in Advanced Materials, (2000), 12, No. 7, pp. 481-494, andreferences therein.

The electronically conductive polymer layer of the invention shouldcontain about 0.1 to about 1000 mg/m² dry coating weight of theelectronically conductive polymer. Preferably, the conductive layershould contain about 1 to about 500 mg/m² dry coating weight of theelectronically conductive polymer. The actual dry coating weight of theconductive polymer applied is determined by the properties of theparticular conductive polymer employed and by the requirements of theparticular application. These requirements include conductivity,transparency, optical density and cost for the layer.

In a preferred embodiment, the layer containing the electronicallyconductive polymer is prepared by applying a mixture comprising:

a) a polythiophene according to Formula I

in a cationic form, wherein each of R1 and R2 independently representshydrogen or a C1-4 alkyl group or together represent an optionallysubstituted C1-4 alkylene group or a cycloalkylene group, preferably anethylene group, an optionally alkyl-substituted methylene group, anoptionally C1-12 alkyl- or phenyl-substituted 1,2-ethylene group, a1,3-propylene group or a 1,2-cyclohexylene group; and n is 3 to 1000;

and

b) a polyanion compound;

It is preferred that the electronically conductive polymer and polyanioncombination is soluble or dispersible in organic solvents or water ormixtures thereof. For environmental reasons, aqueous systems arepreferred. Polyanions used with these electronically conductive polymersinclude the anions of polymeric carboxylic acids such as polyacrylicacids, poly(methacrylic acid), and poly(maleic acid), and polymericsulfonic acids such as polystyrenesulfonic acids and polyvinylsulfonicacids, the polymeric sulfonic acids being preferred for use in thisinvention because they are widely available and water coatable. Thesepolycarboxylic and polysulfonic acids may also be copolymers formed fromvinylcarboxylic and vinylsulfonic acid monomers copolymerized with otherpolymerizable monomers such as the esters of acrylic acid and styrene.The molecular weight of the polyacids providing the polyanionspreferably is 1,000 to 2,000,000 and more preferably 2,000 to 500,000.The polyacids or their alkali salts are commonly available, for exampleas polystyrenesulfonic acids and polyacrylic acids, or they may beproduced using known methods. Instead of the free acids required for theformation of the electronically conducting polymers and polyanions,mixtures of alkali salts of polyacids and appropriate amounts ofmonoacids may also be used. The polythiophene to polyanion weight ratiocan widely vary between 1:99 to 99:1, however, optimum properties suchas high electrical conductivity and dispersion stability and coatabilityare obtained between 85:15 and 15:85, and more preferably between 50:50and 15:85. The most preferred electronically conductive polymers includepoly(3,4-ethylene dioxythiophene styrene sulfonate) which comprisespoly(3,4-ethylene dioxythiophene) in a cationic form andpolystyrenesulfonic acid because of its low optical density, stability,wide availability, high conductivity and ability to be coated fromwater.

Desirable results such as enhanced conductivity of thePEDOT/polystyrenesulfonic acid can be accomplished by incorporating aconductivity enhancing agent (CEA). Preferred CEAs (due to theeffectiveness of reducing the resistivity) are organic compoundscontaining dihydroxy, poly-hydroxy, carboxyl, amide, or lactam groups,such as

(1) those represented by the following Formula II:(OH)_(n)—R—(COX)_(m)  II

wherein m and n are independently an integer of from 1 to 20, R is analkylene group having 2 to 20 carbon atoms, an arylene group having 6 to14 carbon atoms in the arylene chain, a pyran group, or a furan group,and X is —OH or —NYZ, wherein Y and Z are independently hydrogen or analkyl group; or

(2) a sugar, sugar derivative, polyalkylene glycol, or glycerolcompound; or

(3) those selected from the group consisting of N-methylpyrrolidone,pyrrolidone, caprolactam, N-methyl caprolactam, dimethyl sulfoxide orN-octylpyrrolidone; or

(4) a combination of the above.

Particularly preferred conductivity enhancing agents are: sugar andsugar derivatives such as sucrose, glucose, fructose, lactose; sugaralcohols such as sorbitol, mannitol; furan derivatives such as2-furancarboxylic acid, 3-furancarboxylic acid and alcohols. Ethyleneglycol, glycerol, di- or triethylene glycol are most preferred becausethey provide the maximum conductivity enhancement.

The CEA can be incorporated by any suitable method. Preferably the CEAis added to the coating composition comprising the SWCNTs, theelectronically conductive polymer, or both coating compositions.Alternatively, the coated SWCNT layer and electronically conductivepolymer layer can be exposed to the CEA by any suitable method, such aspost-coating wash.

The concentration of the CEA in the coating composition may vary widelydepending on the particular organic compound used and the conductivityrequirements. However, convenient concentrations that may be effectivelyemployed in the practice of the present invention are about 0.5 to about25 weight %; more conveniently 0.5 to 10 and more desirably 0.5 to 5 asit provides the minimum effective amount.

A figure of merit (FOM) can be assigned to the electronically conductivepolymer within the conductive layer. Such FOM values are determined by(1) measuring the visual light transmission (T) and the sheet resistance(R_(S)) of the conductive layer at various thickness values of thelayer, (2) plotting these data in a In (1/T) vs. 1/R_(S) space, and (3)then determining the slope of a straight line best fitting these datapoints and passing through the origin of such a plot. Without beingbound to any particular theory, it is found that ln (1/T) vs. 1/R_(S)plots for electronically conductive polymer layers, particularly thosecomprising polythiophene in a cationic form with a polyanion compound,generate a linear relationship, preferably one passing through theorigin, wherein the slope of such a linear plot is the FOM of theelectronically conductive polymer layer. Without being bound to anyparticular theory, it is also found that lower the FOM value, the moredesirable is the electrical and optical characteristics of theelectronically conductive layer; namely, lower the FOM, lower is theR_(S) and higher is the transparency of the conductive layer. For theinstant invention, FOM values of <100, preferably ≦50, and morepreferably ≦40 is found to generate most desired results for displayapplications,

Visual light transmission value T is determined from the total opticaldensity at 530 nm, after correcting for the contributions of theuncoated substrate. A Model 361T X-Rite densitometer measuring totaloptical density at 530 nm, is best suited for this measurement.

Visual light transmission, T, is related to the corrected total opticaldensity at 530 nm, o.d. (corrected), by the following expression,T=1/(10^(o.d.(corrected)))

The R_(S) value is typically determined by a standard four-pointelectrical probe.

The transparency of the conductive layer of the invention can varyaccording to need. For use as an electrode in a touchscreen, theconductive layer is desired to be highly transparent. Accordingly, thevisual light transmission value T for the conductive layer of theinvention is >65%, preferably ≧70%, more preferably ≧80%, and mostpreferably ≧90%. The conductive layer need not form an integral whole,need not have a uniform thickness and need not be contiguous with thebase substrate. Preferably, the touchscreen of the invention has atransparency of at least 70% in the visible light range.

While the nanotubes and the electronically conductive polymer can beapplied without the addition of a film-forming polymeric binder, afilm-forming binder can be employed to improve the physical propertiesof the layers. In such an embodiment, the layers may comprise from about1 to 95% of the film-forming polymeric binder. However, the presence ofthe film forming binder may increase the overall surface electricalresistivity of the layers. The optimum weight percent of thefilm-forming polymer binder varies depending on the electricalproperties of the carbon nanotubes and the electronically conductivepolymer, the chemical composition of the polymeric binder, and therequirements for the particular touchscreen application.

Polymeric film-forming binders useful in the conductive layers of thisinvention can include, but are not limited to, water-soluble orwater-dispersible hydrophilic polymers such as gelatin, gelatinderivatives, maleic acid or maleic anhydride copolymers, polystyrenesulfonates, cellulose derivatives (such as carboxymethyl cellulose,hydroxyethyl cellulose, cellulose acetate butyrate, diacetyl cellulose,and triacetyl cellulose), polyethylene oxide, polyvinyl alcohol, andpoly-N-vinylpyrrolidone. Other suitable binders include aqueousemulsions of addition-type homopolymers and copolymers prepared fromethylenically unsaturated monomers such as acrylates including acrylicacid, methacrylates including methacrylic acid, acrylamides andmethacrylamides, itaconic acid and its half-esters and diesters,styrenes including substituted styrenes, acrylonitrile andmethacrylonitrile, vinyl acetates, vinyl ethers, vinyl and vinylidenehalides, and olefins and aqueous dispersions of polyurethanes andpolyesterionomers.

Other ingredients that may be included in the conductive layers includebut are not limited to surfactants, defoamers or coating aids, chargecontrol agents, thickeners or viscosity modifiers, antiblocking agents,coalescing aids, crosslinking agents or hardeners, soluble and/or solidparticle dyes, matte beads, inorganic or polymeric particles, adhesionpromoting agents, bite solvents or chemical etchants, lubricants,plasticizers, antioxidants, colorants or tints, and other addenda thatare well-known in the art. Preferred bite solvents can include any ofthe volatile aromatic compounds disclosed in U.S. Pat. No. 5,709,984, as“conductivity-increasing” aromatic compounds, comprising an aromaticring substituted with at least one hydroxy group or a hydroxysubstituted substituents group. These compounds include phenol,4-chloro-3-methyl phenol, 4-chlorophenol, 2-cyanophenol,2,6-dichlorophenol, 2-ethylphenol, resorcinol, benzyl alcohol,3-phenyl-1-propanol, 4-methoxyphenol, 1,2-catechol,2,4-dihydroxytoluene, 4-chloro-2-methyl phenol, 2,4-dinitrophenol,4-chlororesorcinol, 1-naphthol, 1,3-naphthalenediol and the like. Thesebite solvents are particularly suitable for polyester based polymersheets of the invention. Of this group, the most preferred compounds areresorcinol and 4-chloro-3-methyl phenol. Preferred surfactants suitablefor these coatings include nonionic and anionic surfactants. Preferredcross-linking agents suitable for these coatings include silanecompounds such as those disclosed in U.S. Pat. No. 5,370,981.

For use as an electrode in a touchscreen, the conductive layers aredesired to be highly transparent. Accordingly, the visual lighttransmission value T for the conductive layers of the inventionare >65%, preferably ≧70%, more preferably ≧80%, and most preferably≧90%. The conductive layers need not form an integral whole, need nothave a uniform thickness and need not be contiguous with the basesubstrate.

The conductive layers of the invention can be formed on any rigid orflexible substrate. The substrates can be transparent, translucent oropaque, and may be colored or colorless. Preferably, the substrate iscolorless and transparent. Rigid substrates can include glass, metal,ceramic and/or semiconductors. Suitable rigid substrate thickness rangesfrom 50 um-7000 um, depending on the actual material employed for therigid substrate. Flexible substrates, especially those comprising aplastic substrate, are preferred for their versatility and ease ofmanufacturing, coating and finishing.

The flexible plastic substrate can be any flexible polymeric film.“Plastic” means a high polymer, usually made from polymeric syntheticresins, which may be combined with other ingredients, such as curatives,fillers, reinforcing agents, colorants, and plasticizers. Plasticincludes thermoplastic materials and thermosetting materials.

The flexible plastic film must have sufficient thickness and mechanicalintegrity so as to be self-supporting, yet should not be so thick as tobe totally rigid. Suitable flexible plastic substrate thickness rangesfrom 5 um-500 um. To reduce the weight of the touchscreen whileproviding mechanical rigidity and thermal resistance, the thickness ispreferably 50-250 um. Another significant characteristic of the flexibleplastic substrate material is its glass transition temperature (Tg). Tgis defined as the glass transition temperature at which plastic materialwill change from the glassy state to the rubbery state. It may comprisea range before the material may actually flow. Suitable materials forthe flexible plastic substrate include thermoplastics of a relativelylow glass transition temperature, for example up to 150° C., as well asmaterials of a higher glass transition temperature, for example, above150° C. The choice of material for the flexible plastic substrate woulddepend on factors such as manufacturing process conditions, such asdeposition temperature, and annealing temperature, as well aspost-manufacturing conditions such as in a process line of a displaysmanufacturer. Certain of the plastic substrates discussed below canwithstand higher processing temperatures of up to at least about 200°C., some up to 300°-350° C., without damage.

Typically, the flexible plastic substrate is a polyester includingpolyethylene terephthalate (PET), polyethylene naphthalate (PEN),polyester ionomer, polyethersulfone (PES), polycarbonate (PC),polysulfone, a phenolic resin, an epoxy resin, polyester, polyimide,polyetherester, polyetheramide, cellulose nitrate, cellulose acetate,poly(vinyl acetate), polystyrene, polyolefins including polyolefinionomers, polyamide, aliphatic polyurethanes, polyacrylonitrile,polytetrafluoroethylenes, polyvinylidene fluorides, poly(methyl(x-methacrylates), an aliphatic or cyclic polyolefin, polyarylate (PAR),polyetherimide (PEI), polyethersulphone (PES), polyimide (PI), Teflonpoly(perfluoro-alboxy) fluoropolymer (PFA), poly(ether ether ketone)(PEEK), poly(ether ketone) (PEK), poly(ethylenetetrafluoroethylene)fluoropolymer (PETFE), and poly(methyl methacrylate)and various acrylate/methacrylate copolymers (PMMA) natural andsynthetic paper, resin-coated or laminated paper, voided polymersincluding polymeric foam, microvoided polymers and microporousmaterials, or fabric, or any combinations thereof.

Aliphatic polyolefins may include high density polyethylene (HDPE), lowdensity polyethylene (LDPE), and polypropylene, including orientedpolypropylene (OPP). Cyclic polyolefins may includepoly(bis(cyclopentadiene)). A preferred flexible plastic substrate is acyclic polyolefin or a polyester. Various cyclic polyolefins aresuitable for the flexible plastic substrate. Examples include Arton®made by Japan Synthetic Rubber Co., Tokyo, Japan; Zeanor T made by ZeonChemicals L.P., Tokyo Japan; and Topas® made by Celanese A. G., KronbergGermany. Arton is a poly(bis(cyclopentadiene)) condensate that is a filmof a polymer. Alternatively, the flexible plastic substrate can be apolyester. A preferred polyester is an aromatic polyester such asArylite. Although the substrate can be transparent, translucent oropaque, for most display applications transparent members comprisingtransparent substrate(s) are preferred. Although various examples ofplastic substrates are set forth above, it should be appreciated thatthe flexible substrate can also be formed from other materials such asflexible glass and ceramic.

The most preferred flexible plastic substrate is polyester because ofits superior mechanical and thermal properties as well as itsavailability in large quantity at a moderate price. The particularpolyester chosen for use can be a homo-polyester or a copolyester, ormixtures thereof as desired. The polyester can be crystalline oramorphous or mixtures thereof as desired. Polyesters are normallyprepared by the condensation of an organic dicarboxylic acid and anorganic diol and, therefore, illustrative examples of useful polyesterswill be described herein below in terms of these diol and dicarboxylicacid precursors.

Polyesters which are suitable for use in this invention are those whichare derived from the condensation of aromatic, cycloaliphatic, andaliphatic diols with aliphatic, aromatic and cycloaliphatic dicarboxylicacids and may be cycloaliphatic, aliphatic or aromatic polyesters.Exemplary of useful cycloaliphatic, aliphatic and aromatic polyesterswhich can be utilized in the practice of their invention arepoly(ethylene terephthalate), poly(cyclohexlenedimethylene),terephthalate)poly(ethylene dodecate), poly(butylene terephthalate),poly(ethylene naphthalate), poly(ethylene(2,7-naphthalate)),poly(methaphenylene isophthalate), poly(glycolic acid), poly(ethylenesuccinate), poly(ethylene adipate), poly(ethylene sebacate),poly(decamethylene azelate), poly(ethylene sebacate), poly(decamethyleneadipate), poly(decamethylene sebacate), poly(dimethylpropiolactone),poly(para-hydroxybenzoate) (Ekonol), poly(ethylene oxybenzoate)(A-tell), poly(ethylene isophthalate), poly(tetramethyleneterephthalate, poly(hexamethylene terephthalate), poly(decamethyleneterephthalate), poly(1,4-cyclohexane dimethylene terephthalate) (trans),poly(ethylene 1,5-naphthalate), poly(ethylene 2,6-naphthalate),poly(1,4-cyclohexylene dimethylene terephthalate), (Kodel) (cis), andpoly(1,4-cyclohexylene dimethylene terephthalate (Kodel) (trans).Polyester compounds prepared from the condensation of a diol and anaromatic dicarboxylic acid is preferred for use in this invention.Illustrative of such useful aromatic carboxylic acids are terephthalicacid, isophthalic acid and an α-phthalic acid,1,3-napthalenedicarboxylic acid, 1,4 napthalenedicarboxylic acid,2,6-napthalenedicarboxylic acid, 2,7-napthalenedicarboxylic acid,4,4′-diphenyldicarboxylic acid, 4,4′-diphenysulfphone-dicarboxylic acid,1,1,3-trimethyl-5-carboxy-3-(p-carboxyphenyl)-idane, diphenyl ether4,4′-dicarboxylic acid, bis-p(carboxy-phenyl) methane, and the like. Ofthe aforementioned aromatic dicarboxylic acids, those based on a benzenering (such as terephthalic acid, isophthalic acid, orthophthalic acid)are preferred for use in the practice of this invention. Amongst thesepreferred acid precursors, terephthalic acid is particularly preferredacid precursor.

Preferred polyesters for use in the practice of this invention includepoly(ethylene terephthalate), poly(butylene terephthalate),poly(1,4-cyclohexylene dimethylene terephthalate) and poly(ethylenenaphthalate) and copolymers and/or mixtures thereof. Among thesepolyesters of choice, poly(ethylene terephthalate) is most preferredbecause of its low cost, high transparency, and low coefficient ofthermal expansion.

The aforesaid substrate can comprise a single layer or multiple layersaccording to need. The multiplicity of layers may include any number ofauxiliary layers such as hard coat layers, antistatic layers, tie layersor adhesion promoting layers, abrasion resistant layers, curl controllayers, conveyance layers, barrier layers, splice providing layers, UVabsorption layers, optical effect providing layers, such asantireflective and antiglare layers, waterproofing layers, adhesivelayers, and the like.

In a preferred embodiment the touch side electrode further comprises ananti-glare layer, anti-reflection layer, ultra violet light absorbinglayer, or abrasion resistant hard coat layer on the side of thesubstrate opposite to the electrically conductive layers. Preferably,the anti-glare or hard coat layer has a pencil hardness (using theStandard Test Method for Hardness by Pencil Test ASTM D3363) of at least1H, more preferably a pencil hardness of 2H to 8H.

Particularly effective hard coat layers for use in the present inventioncomprise radiation or thermally cured compositions, and preferably thecomposition is radiation cured. Ultraviolet (UV) radiation and electronbeam radiation are the most commonly employed radiation curing methods.UV curable compositions are particularly useful for creating theabrasion resistant layer of this invention and may be cured using twomajor types of curing chemistries, free radical chemistry and cationicchemistry. Acrylate monomers (reactive diluents) and oligomers (reactiveresins and lacquers) are the primary components of the free radicalbased formulations, giving the cured coating most of its physicalcharacteristics. Photo-initiators are required to absorb the UV lightenergy, decompose to form free radicals, and attack the acrylate groupC═C double bond to initiate polymerization. Cationic chemistry utilizescycloaliphatic epoxy resins and vinyl ether monomers as the primarycomponents. Photo-initiators absorb the UV light to form a Lewis acid,which attacks the epoxy ring initiating polymerization. By UV curing ismeant ultraviolet curing and involves the use of UV radiation ofwavelengths between 280 and 420 nm preferably between 320 and 410 nm.

Examples of UV radiation curable resins and lacquers usable for theabrasion layer useful in this invention are those derived from photopolymerizable monomers and oligomers such as acrylate and methacrylateoligomers (the term “(meth)acrylate” used herein refers to acrylate andmethacrylate), of polyfunctional compounds, such as polyhydric alcoholsand their derivatives having (meth)acrylate functional groups such asethoxylated trimethylolpropane tri(meth)acrylate, tripropylene glycoldi(meth)acrylate, trimethylolpropane tri(meth)acrylate, diethyleneglycol di(meth)acrylate, pentaerythritol tetra(meth)acrylate,pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate,1,6-hexanediol di(meth)acrylate, or neopentyl glycol di(meth)acrylateand mixtures thereof, and acrylate and methacrylate oligomers derivedfrom low-molecular weight polyester resin, polyether resin, epoxy resin,polyurethane resin, alkyd resin, spiroacetal resin, epoxy acrylates,polybutadiene resin, and polythiol-polyene resin, and the like andmixtures thereof, and ionizing radiation-curable resins containing arelatively large amount of a reactive diluent. Reactive diluents usableherein include monofunctional monomers, such as ethyl(meth)acrylate,ethylhexyl(meth)acrylate, styrene, vinyltoluene, and N-vinylpyrrolidone,and polyfunctional monomers, for example, trimethylolpropanetri(meth)acrylate, hexanediol (meth)acrylate, tripropylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritoltri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, or neopentyl glycol di(meth)acrylate.

Among others, in the present invention, conveniently used radiationcurable lacquers include urethane(meth)acrylate oligomers. These arederived from reacting diisocyanates with a oligo(poly)ester oroligo(poly)ether polyol to yield an isocyanate terminated urethane.Subsequently, hydroxy terminated acrylates are reacted with the terminalisocyanate groups. This acrylation provides the unsaturation to the endsof the oligomer. The aliphatic or aromatic nature of the urethaneacrylate is determined by the choice of diisocyanates. An aromaticdiisocyanate, such as toluene diisocyanate, will yield an aromaticurethane acrylate oligomer. An aliphatic urethane acrylate will resultfrom the selection of an aliphatic diisocyanate, such as isophoronediisocyanate or hexyl methyl diisocyanate. Beyond the choice ofisocyanate, polyol backbone plays a pivotal role in determining theperformance of the final the oligomer. Polyols are generally classifiedas esters, ethers, or a combination of these two. The oligomer backboneis terminated by two or more acrylate or methacrylate units, which serveas reactive sites for free radical initiated polymerization. Choicesamong isocyanates, polyols, and acrylate or methacrylate terminationunits allow considerable latitude in the development of urethaneacrylate oligomers. Urethane acrylates like most oligomers, aretypically high in molecular weight and viscosity. These oligomers aremultifunctional and contain multiple reactive sites. Because of theincreased number of reactive sites, the cure rate is improved and thefinal product is cross-linked. The oligomer functionality can vary from2 to 6.

Among others, conveniently used radiation curable resins includepolyfunctional acrylic compounds derived from polyhydric alcohols andtheir derivatives such as mixtures of acrylate derivatives ofpentaerythritol such as pentaerythritol tetraacrylate andpentaerythritol triacrylate functionalized aliphatic urethanes derivedfrom isophorone diisocyanate. Some examples of urethane acrylateoligomers used in the practice of this invention that are commerciallyavailable include oligomers from Sartomer Company (Exton, Pa.). Anexample of a resin that is conveniently used in the practice of thisinvention is CN 968® from Sartomer Company.

A photo polymerization initiator, such as an acetophenone compound, abenzophenone compound, Michler's benzoyl benzoate, α-amyloxime ester, ora thioxanthone compound and a photosensitizer such as n-butyl amine,triethylamine, or tri-n-butyl phosphine, or a mixture thereof isincorporated in the ultraviolet radiation curing composition. In thepresent invention, conveniently used initiators are 1-hydroxycyclohexylphenyl ketone and 2-methyl-1-[4-(methyl thio)phenyl]-2-morpholinopropanone-1.

The UV polymerizable monomers and oligomers are coated and dried, andsubsequently exposed to UV radiation to form an optically clearcross-linked abrasion resistant layer. The preferred UV cure dosage isbetween 50 and 1000 mJ/cm².

The thickness of the hard coat layer is generally about 0.5 to 50micrometers preferably 1 to 20 micrometers, more preferably 2 to 10micrometers.

An antiglare layer provides a roughened or textured surface that is usedto reduce specular reflection. All of the unwanted reflected light isstill present, but it is scattered rather than specularly reflected. Forthe purpose of the present invention, the antiglare layer preferablycomprises a radiation cured composition that has a textured or roughenedsurface obtained by the addition of organic or inorganic (matting)particles or by embossing the surface. The radiation cured compositionsdescribed hereinabove for the hard coat layer are also effectivelyemployed in the antiglare layer. Surface roughness is preferablyobtained by the addition of matting particles to the radiation curedcomposition. Suitable particles include inorganic compounds having anoxide, nitride, sulfide or halide of a metal, metal oxides beingparticularly preferred. As the metal atom, Na, K, Mg, Ca, Ba, Al, Zn,Fe, Cu, Ti, Sn, In, W, Y, Sb, Mn, Ga, V, Nb, Ta, Ag, Si, B, Bi, Mo, Ce,Cd, Be, Pb and Ni are suitable, and Mg, Ca, B and Si are morepreferable. An inorganic compound containing two types of metal may alsobe used. A particularly preferable inorganic compound is silicondioxide, namely silica.

The polymer substrate can be formed by any method known in the art suchas those involving extrusion, coextrusion, quenching, orientation, heatsetting, lamination, coating and solvent casting. It is preferred thatthe polymer substrate is an oriented sheet formed by any suitable methodknown in the art, such as by a flat sheet process or a bubble or tubularprocess. The flat sheet process involves extruding or coextruding thematerials of the sheet through a slit die and rapidly quenching theextruded or coextruded web upon a chilled casting drum so that thepolymeric component(s) of the sheet are quenched below theirsolidification temperature.

The quenched sheet is then biaxially oriented by stretching in mutuallyperpendicular directions at a temperature above the glass transitiontemperature of the polymer(s). The sheet may be stretched in onedirection and then in a second direction or may be simultaneouslystretched in both directions. The preferred stretch ratio in anydirection is at least 3:1. After the sheet has been stretched, it isheat set by heating to a temperature sufficient to crystallize thepolymers while restraining to some degree the sheet against retractionin both directions of stretching.

The polymer sheet may be subjected to any number of coatings andtreatments, after extrusion, coextrusion, orientation, etc. or betweencasting and full orientation, to improve its properties, such asprintability, barrier properties, heat-sealability, spliceability,adhesion to other substrates and/or imaging layers. Examples of suchcoatings can be acrylic coatings for printability, polyvinylidene halidefor heat seal properties, etc. Examples of such treatments can be flame,plasma and corona discharge treatment, ultraviolet radiation treatment,ozone treatment and electron beam treatment to improve coatability andadhesion. Further examples of treatments can be calendaring, embossingand patterning to obtain specific effects on the surface of the web. Thepolymer sheet can be further incorporated in any other suitablesubstrate by lamination, adhesion, cold or heat sealing, extrusioncoating, or any other method known in the art.

Dielectric spacers, that may be dot-shaped for example, are provided onthe surface of the conductive layer at regular distances, such as everyfew millimeters. The spacers are made of polymeric resin, and eachspacer is about 10 um in height and 10 um to 50 um in diameter. Suitablepolymeric resin that may be employed to prepare the spacers includelight or thermal hardened epoxy, acrylated-urethanes, acrylic, and othercompositions well known by the skilled artisan. The spacersalternatively may be filled with nanoparticles such as silica, alumina,zinc oxide and others in order to modify the physical properties of thespacers.

Alternatively, it is known to form the spacers for example by sprayingthrough a mask or pneumatically sputtering small diameter transparentglass or polymer particles, as described in U.S. Pat. No. 5,062,198issued to Sun, Nov. 5, 1991. The transparent glass or polymer particlesare typically 45 microns in diameter or less and mixed with atransparent polymer adhesive in a volatile solvent before application.The spacers may also be prepared by lithographic techniques that arewell known in the art.

FIG. 3 shows another embodiment of a resistive-type touchscreen of theinvention 59 having electrodes 60 and 70. Electrode 60 may be the touchside electrode and electrode 70 may be the device side electrode oralternatively that electrode 70 may be the touch side electrode andelectrode 60 may be the device side electrode. Electrode 70 comprises inorder, an insulating substrate 63, a buried electrically conductivelayer 65 in contact with said substrate, and an exposed electricallyconductive layer 67. Electrode 60 comprises in order, an insulatingsubstrate 62 and an exposed electrically conductive layer 66 in contactwith said substrate. Wherein said exposed electrically conductive layers66 and 67 are adjacent and separated by dielectric spacers 68. In theembodiment depicted in FIG. 3, either exposed electrically conductivelayer 66 or 67 (but not both) comprises carbon nanotubes. Suitablecarbon nanotubes have been described in detail herein above, The otherexposed electrically conductive layer that does not comprise carbonnanotubes may comprise at least one material from the group consistingof electronically conductive polymers, transparent conducting oxides andtransparent metal films.

The buried electrically conductive layer 65 may comprise at least onematerial from the group consisting of carbon nanotubes, electronicallyconductive polymers, transparent conducting oxides and transparent metalfilms

Preferably, the buried electrically conductive layer has a sheetresistance of between 10 and 10,000 Ohm per square and the exposedelectrically conductive layers have a sheet resistance of between 100and 10⁶ Ohm per square.

FIG. 4 shows yet another embodiment of a resistive-type touchscreen ofthe invention 129 having electrodes 130 and 140. Electrode 130 may bethe touch side electrode and electrode 140 may be the device sideelectrode or alternatively that electrode 130 may be the touch sideelectrode and electrode 140 may be the device side electrode. Electrode140 comprises in order, an insulating substrate 133, a buriedelectrically conductive layer 135 in contact with said substrate, and anexposed electrically conductive layer 137. Electrode 130 comprises inorder, an insulating substrate 132, a buried electrically conductivelayer 134 in contact with said substrate and an exposed electricallyconductive layer 136. Wherein said exposed electrically conductivelayers 136 and 137 are adjacent and separated by dielectric spacers 138.In the embodiment depicted in FIG. 4, either exposed electricallyconductive layer 136 or 137 (but not both) comprises carbon nanotubes.Suitable carbon nanotubes have been described in detail herein above,The other exposed electrically conductive layer that does not comprisecarbon nanotubes may comprise at least one material from the groupconsisting of electronically conductive polymers, transparent conductingoxides and transparent metal films.

The buried electrically conductive layers 134 and 135 may be the same ordifferent in composition and comprise at least one material from thegroup consisting of carbon nanotubes, electronically conductivepolymers, transparent conducting oxides and transparent metal films

Preferably, the buried electrically conductive layer has a sheetresistance of between 10 and 10,000 Ohm per square and the exposedelectrically conductive layers have a sheet resistance of between 100and 10⁶ Ohm per square. Preferably, the electronically conductive layercomprising carbon nanotubes has a sheet resistance of between 10² to 10⁶Ohm per square.

Resistive touchscreens of the invention preferably are mechanicallyrobust to point actuations by objects (plastic or metal stylus, fingersetc.). A touchscreen is activated or actuated when the touch side anddevice side electrodes contact. Over time, repetitive contact and theforce applied during such contact damage prior art touchscreens. Suchdamage requires that increasingly larger forces are necessary to actuatethe touchscreen. In a preferred embodiment of the instant invention, theforce required to actuate a point on the touchscreen does not change bymore than 500 percent over 500,000 single point actuations. Morepreferably, the force required to actuate the touchscreen does notchange by more than 100 percent and most preferably more than 50percent. A single point actuation is the application of an object at asingle point on the touchscreen to activate such touchscreen.

The conventional construction of a resistive touch screen involves thesequential placement of materials upon the substrates. The substratesare formed as described herein above, then uniform conductive layers areapplied to the substrates. The bus bars are applied to the touch sideelectrode and the spacers and bus bars are applied to the device sideelectrode and, finally, the touch side electrode is attached to thedevice side electrode.

FIG. 5 is an exploded view showing the construction of a touchscreen 100of the present invention. As shown in FIG. 5, the touchscreen 100 ismainly composed of a touch side electrode 110 and a device sideelectrode 120. The touch side electrode 110 and the device sideelectrode 120 are set facing each other, with dielectric spacers 30being placed in between them so that an air gap is formed between thesubstrates.

As shown in FIG. 5, the touch side electrode 110 is provided with a pairof bus bars 141 and 142 which are adhered to the exposed electricallyconductive layer along its ends to be opposed to each other in the Adirection. The touch side electrode 110 is also provided with a pair ofconnector electrodes 143 and 144 at its edge, to which connectors (notshown) are connected. The bus bars 141 and 142 are connected to the pairof connector electrodes 143 and 144 via wiring patterns 145 and 146. Thebus bars, connector electrodes, and wiring patterns comprise highconductivity materials. Suitable high conductivity materials includecarbon black, silver, gold, platinum, palladium, copper or combinationsof these materials. These materials may be applied by vacuum deposition,inkjet printing, thermal transfer, silk screen printing or othermethods. These materials may be thermally or light hardened.

As shown in FIG. 5, the device side electrode 120 is provided with apair of bus bars 251 and 252 which are adhered to the exposedelectrically conductive layer along its ends to be opposed to each otherin the B direction that is perpendicular to the A direction. The deviceside electrode 120 is also provided with a pair of connector electrodes253 and 254 at its edge, to which connectors (not shown) are connected.The pair of bus bars 251 and 252 are connected to the pair of connectorelectrodes 253 and 254 via wiring patterns 255 and 256. Dot-shapedspacers 30, for example, are provided on the surface of the exposedconductive layer deposed on device side electrode 120, such as every fewmillimeters. The spacers 30 are made of light-hardening acrylic resinfor example, and each spacer is about 10 μm in height and 10 μm to 50 μmin diameter. Respective outer regions of the touch side electrode 110and the device side electrode 120 are bonded together by an adhesive 40.

Touchscreens prepared as described above may be employed in a variety ofdisplay devices. In a preferred embodiment, the display device comprisesa liquid crystal display (LCD). Conveniently, the touchscreen of theinvention may be adhesively attached to a polarizer plate within theliquid crystal display device.

The conductive layers of the invention can be applied by any methodknown in the art. Particularly preferred methods include coating from asuitable liquid medium coating composition by any well known coatingmethod such as air knife coating, gravure coating, hopper coating,roller coating, spray coating, electrochemical coating, inkjet printing,flexographic printing, and the like. The first electrically conductivelayer and the exposed electrically conductive layer may be appliedsequentially or simultaneously.

Alternatively, the conductive layers can be transferred to a receivermember comprising the substrate from a donor member by the applicationof heat and/or pressure. An adhesive layer may be preferably presentbetween the donor member and the receiver member substrate to facilitatetransfer. The two conductive layers may be applied onto each substratesimultaneously from a single donor element or sequentially from twoseparate donor members as described in copending commonly assigned U.S.patent application Ser. No. 10/969,889 filed Oct. 21, 2004, Majumdar etal, Ser. No. 11/062,416 filed Feb. 22, 2005, Irvin et al., and Ser. No.11/022,155, filed Dec. 22, 2004, Majumdar et al.

Besides the conductive layers of the invention, the aforementionedthermal transfer element may comprise a number of auxiliary layers.These auxiliary layers may include radiation absorption layers, whichcan be a light to heat conversion layer, interlayer, release layer,adhesion promoting layer, operational layer (which is used in theoperation of a device), non-operational layer (which is not used in theoperation of a device but can facilitate, for example, transfer of atransfer layer, protection from damage and/or contact with outsideelements).

Thermal transfer of the conductive layers of the invention can beaccomplished by the application of directed heat on a selected portionof the thermal transfer element. Heat can be generated using a heatingelement (e.g., a resistive heating element), converting radiation (e.g.,a beam of light) to heat, and/or applying an electrical current to alayer of thermal transfer element to generate heat.

Typically, a very smooth surface, with low roughness (Ra) is desired formaximizing optical and barrier properties of the coated substrate.Preferred Ra values for the conductive layer of the invention is lessthan 1000 nm, more preferably less than 100 nm, and most preferably lessthan 20 nm. However, it is to be understood that if for some applicationa rougher surface is required higher Ra values can be attained withinthe scope of this invention, by any means known in the art.

EXAMPLES

The following non-limiting examples further describe the practice of theinstant invention.

Examples of Single and Multilayer Conductors Used to Construct TouchSwitches: Table I

Sheet Coating Resistance Com- Coating Conductor Substrate # of (ohms/position ID Type Type Layers square Used A Bekaert ITO 102 um PET 1 300NA B Keytec ITO 203 um PET 1 400 NA C 344 mg/m² 102 um PET 1 438 IBaytron P AG D 344 mg/m² 102 um 1 463 H Baytron P AG E First layer 172102 um PET 2 775 H first, M mg/m² Baytron second P AG with 8 mg/m² SWCNT2^(nd) layer F First layer 344 102 um PET 2 470 H first, M mg/m2 Baytronsecond P AG with 8 mg/m² SWCNT 2^(nd) layer G SWCNT layer 102 um PET 1670 V with 64.6 mg/m2 SWCNT

Coatings A & B were supplied by the vendors Bekaert and Keytec,respectively. The Bekaert ITO is coated onto a 102 um PET substrate. TheKeytec sample had a coating on the opposite surface of the ITO on PET.The PET used in the Keytec sample is a 203 um substrate.

Coatings C, D, E and F were produced as follows. The followingingredients were used to form the coating composition for forming themultilayer examples and single layer comparative examples:

Ingredients for Coating Composition

(a) Baytron P AG: aqueous dispersion of electronically conductivepolythiophene and polyanion, namely, poly(3,4-ethylene dioxythiophenestyrene sulfonate), supplied by H.C. Starck;

(b) TX-100: nonionic surfactant coating aid supplied by Rohm & Haas;

(c) Ethanol;

(d) diethylene glycol: conductivity enhancing agent supplied by Aldrich;

(e) Silquest A 187: 3-glycidoxy-propyltrimethyoxysilane supplied byCrompton Corporation and

(f) SWCNTs: P3 swcnt product supplied by Carbon Solutions

The following coating composition A was prepared for coating suitablesubstrates to form the multilayer conductor examples: Coatingcomposition H Baytron P AG (1.3% active in aqueous) 266 g TX-100 1.5 gDiethylene glycol 12 g Silquest A 187 5.4 g High purity water 28.47 g

Coating composition I Baytron P AG (1.3% active in aqueous) 266 g TX-1001.5 g Diethylene glycol 12 g High purity water 33.87 g

Coating composition M P3 SWCNT - 0.075 wt % in water TX-100 - 0.015 wt %in water Ethanol - 25 wt % in water Balance high purity water

Coating composition V P3 SWCNT - 0.10 wt % in water Ethanol - 25 wt % inwater Balance high purity water

The substrate used was polyethylene terephthalate (PET). The PETsubstrate was photographic grade with a thickness of 102 μm and surfaceroughness Ra of 0.5 nm. On the coating side (frontside) of the PET athin vinylidene chloride copolymer primer layer was applied at athickness of 80 nm. The coating composition H or I was applied to thefrontside surface of the substrate by a hopper at different wetcoverages to give dry coverages of Baytron P AG of between 170 mg/m² and350 mg/m², and each coating was dried at 82° C. for five minutes. Whenappropriate, in a second pass, coating composition M was applied overthe dried Baytron P AG coating (previously deposited by coatingcomposition H) at a single wet coverage to give a dry coverage of SWCNTof 8 mg/m². In this manner, examples of multilayer conductors werecreated as per the instant invention, wherein conductive layers havingdifferent dry coverage of electronically conductive Baytron P AG werecoated on the surface of the substrate in one layer and a second layerof SWCNT was applied over the Baytron P AG. The coating composition Vwas applied to the frontside surface of the substrate by a hopper atdifferent wet coverages to give dry coverages of SWCNT of between 10mg/m² and 100 mg/m², and each coating was dried at 82° C. for fiveminutes. The sheet resistance, R_(S), (ohms/square) of the coatings wasmeasured by a 4-point electrical probe.

In order to evaluate the robustness of the single and multilayerconductors used as asymmetric electrodes of the instant invention, smalltouchscreens (termed touch switch hereafter) were created and tested asdescribed below.

Turning to FIG. 8 Single and Multilayer conductor material combinationswere evaluated for mechanical robustness by constructing a singlepole-single throw touchscreen as follows:

A 1.27 cm×3.8 cm “bottom” (device side) conductive coating 302 onflexible substrate was cut from a larger coated sheet. The bottomconductive coating 302 was attached, conductive side up, along one longedge of a 25 mm×75 mm glass microscope slide 301. The bottom conductivecoating 302 was retained by (2) 3.8 cm lengths of copper foil 304 tape(3M 1181 EMI Shielding Tape) applied across the 1.27 cm ends of the filmstrip and extending beyond the 2.5 cm dimension of the slide. The excesstape was folded back on itself to form an attachment tab for electricalconnection.

Sixteen spacer dots 303 of non-critical dimension were applied in a 4×4matrix over the central 1.27 cm×1.27 cm square area of the bottomconductor. Spacer dot 303 dimensions can be called out as 0.1-1.0 mmdiameter, preferably 0.1-0.3 mm diameter for uniformity of actuationforce. Dots were comprised of epoxy (Devcon No. 14250) applied by handusing a pointed applicator. A 1.27 cm square of non-conducting doublesided tape 305 (Polyken) was applied to the glass slide adjacent to thespacer dot matrix.

A 1.27 cm×3.8 cm strip of “top” (touch side) conductive coating 306 onflexible substrate was attached, conductive side down, over the doublesided tape to form a “T” arrangement with one end of the strip coveringthe spacer dot array and the other end extending beyond the 2.54 cmdimension of the glass slide. A 2.54 cm length of conductive copper foil304 tape was wrapped around the overhanging top conductor to form anelectrical attachment.

A line of silver conducting paint (Ernest Fullam No. 14810) was appliedacross the copper tape/conductor layer interfaces to augment theconductive adhesive of the foil tape.

Single Point Actuation Testing Method

Completed touchscreens were placed in the stationary nest of a testapparatus consisting of a brushless linear motor and force mode motioncontrol. A polyurethane 0.79 cm spherical radius hemisphere switchactuating “finger” (McMaster-Carr # 95495K1) is mounted to a load cell,which is in turn mounted to the moving linear motor stage. The fingerwas pressed against the switch with a force profile consisting of zeroforce for 125 mS, a linear ramp to peak force over 125 mS, a hold atpeak force for 125 mS, and a linear load reduction over 125 mS. Theloading pattern was repeated continuously at 2 actuations/second for theduration of the test. Peak force was set for 200-300 grams force. Thetouchscreen was electrically loaded by supplying a regulated 5Vdifferential between the top and bottom conductors. At the mid point ofthe peak force period, the connections to the test device wereelectronically switched to force current in the reverse direction duringthe second half of the actuation cycle. Current flow through thetouchscreen was monitored as a function of time and actuation force.

The touchscreen was considered to make and break at a resistance of orbelow 12 kOhms. The data recorded were on-state resistance and the forcerequired to achieve an on state e.g. to make a switch in state. Atouchscreen was considered to fail when routinely exceeding 12 kOhmson-state resistance.

Comparative Example 1 Single Layer ITO Conductor Touchscreen

A touchscreen was constructed using Coating A from Table I (BekaertITO—Lot #5189376). The single point actuation testing was performed andgave the results indicated in FIGS. 9 and 10 below. The single layer ofBekaert ITO began to show significant changes in force to actuate asearly as completing 10,000 single point actuations (SPA). The on-stateresistance showed significant deviation as early as 85,000 SPA. At88,000 SPA, the single layer of Bekaert ITO routinely exceeded anon-state resistance of 12,000 ohms and failed. Addtionally, by 88,000SPA the actuation force was highly scattered and not stable. It is clearfrom the figures that as the number of actuations increase, thereliability of the touchscreen decreases as evidenced by the significantscatter in the data which corresponds to higher forces required toactuate and increasing on-state resistance which are not desirable.Additionally, the scattered data illustrates potential problems withresolution of point selection.

Comparative Example 2 Single Layer Baytron P AG Conductor Touchscreen

A touchscreen was constructed using Coating C from Table I (344 mg/m²Baytron P AG). The SPA testing was performed and gave the resultsindicated in FIGS. 11 and 12 below. The single layer of Baytron P AGbegan to show significant changes in force to actuate as early ascompleting 3,000 single point actuations (SPA). The on-state resistanceshowed significant deviation as early as 6,000 SPA. At 6,000 SPA, thesingle layer of Baytron P AG permanently exceeded an on-state resistanceof 12,000 ohms, reaching a value of 100,000+ ohms. Addtionally, by 6,000SPA the actuation force experienced an exponential increase and failedshortly thereafter. It is clear from the figures that as the number ofactuations increase, the reliability of the single layer Baytron P AGbased touchscreen decreases as evidenced by the significant scatter inthe data which corresponds to higher forces required to actuate andincreasing on-state resistance which are not desirable. Additionally,the scattered data illustrates potential problems with resolution ofpoint selection.

Comparative Example 3 Single Layer Baytron P AG (Containing CrosslinkingAgent) Conductor Touchscreen

A touchscreen was constructed using Coating D from Table I (344 mg/m²Baytron P AG w/Silquest A187). The SPA testing was performed. Thistouchscreen experienced similar on-state resistance and actuation forceprofiles as Comparative Example 2 and failed after 17,000 SPA. It isclear that as the number of actuations increase, the reliability of thesingle layer Baytron P AG with hardening agent based touchscreendecreases as evidenced by the significant scatter in the data whichcorresponds to higher forces required to actuate and increasing on-stateresistance which are not desirable. Additionally, the scattered dataillustrates potential problems with resolution of point selection.

Comparative Example 4 Single Layer Keytec ITO Conductor Touchscreen

A touchscreen was constructed using Coating B from Table I (400ohm/square Keytec ITO). The SPA testing was performed and gave theresults indicated in FIGS. 13 and 14 below. The single layer of KeytecITO had a linear increase in the force to actuate and began to showsignificant changes in force to actuate as early as completing 25,000SPA. The on-state resistance showed significant deviation as early as35,000 SPA. At 38,000 SPA, the single layer of Keytec ITO permanentlyexceeded an on-state resistance of 12,000 ohms, reaching a value of13,000+ ohms and continued to increase to values as high as 10,000,000ohms. Addtionally, by 30,000 SPA the actuation force experienced anexponential increase and failed shortly thereafter with significantscatter in the force to actuate. It is clear from the figures that asthe number of actuations increase, the reliability of the single layerKeytec ITO based touchscreen decreases as evidenced by the significantscatter in the data which corresponds to higher forces required toactuate and increasing on-state resistance which are not desirable.Additionally, the scattered data illustrates potential problems withresolution of point selection.

Comparative Example 5 Asymmetric Electrode Touch Switch with Keytec ITOand Baytron P AG as Opposing Electrodes

A touchscreen was constructed using Coating B from Table I (400ohm/square Keytec ITO) as one electrode and using Coating C from Table I(344 mg/m² Baytron P AG). The SPA testing was performed and gave theresults indicated in FIG. 15. Surprisingly, this touchscreen failedimmediately due to displaying diode behavior as evidenced by the largedifferences in the measured forward and reverse resistances of thetouchscreen. A touchscreen made of such electrode combinations does notfunction. It is clear from the figure that the reliability of theBaytron P AG and Keytec ITO asymmetric electrode combination basedtouchscreen is not good as evidenced by the large separation in on-stateresistance values for the forward and reverse measured resistance of thetouchswitch. Additionally, the after only 250 cycles the resistance offorward and reverse become so high that the device is not functional.

Instant Invention Example 1 Asymmetric Electrode Touch Switch withBekaert ITO and Single Wall Carbon Nanotubes

A touchscreen was constructed using Coating A from Table I (BekaertITO—Lot #5189376) as one electrode and Coating SWCNT from Table I (SWCNTat 64.6 mg/m²) as the second, opposing electrode. The single pointactuation testing was performed and gave the results indicated in FIGS.16 and 17 below. The asymmetric electrode touchscreen began to showchanges in force to actuate after completing 50,000 single pointactuations (SPA). The on-state resistance showed deviation after 60,000SPA. At approximately 400,000 SPA, the asymmetric electrode touchscreenof Bekaert ITO and SWCNTs routinely exceeded an on-state resistance of12,000 ohms. It is important to note that when contrasted withComparative Example 1, the usage of the asymmetric electrodearchitecture and corresponding materials significantly improved thelifetime of the Bekaert ITO for SPA lifetime. It is also evidenced byInstant Invention Example 1 that the force to actuate does not displaysuch wide swings in value as does Comparative Example 1, e.g. at 50,000cycles for Comparative Example 1 there are already swings as much as 100g of force as compared to Instant Invention Example 1 with only as muchas 20-30 g of force. Further, the rate of increase for force to actuateis significantly faster in Comparative Example 1.

Instant Invention 2 Asymmetric Electrode Touch Switch with Baytron P AG(Containing Crosslinking Agent) and Single Wall Carbon Nanotubes

A touchscreen was constructed using Coating D from Table I (344 mg/m²Baytron P AG w/Silquest A187) as one electrode and Coating SWCNT fromTable I (SWCNT at 64.6 mg/m²) as the second, opposing electrode. Thesingle point actuation testing was performed and gave the resultsindicated in FIGS. 18 and 19 below. This asymmetric electrodetouchscreen demonstrated essentially no change in the force to actuateafter completing 1.1 Million SPA. In fact, there was a small decrease inthe force needed to actuate the touchscreen, as compared to thecomparative examples that all exhibit increases in the force to actuateas the number of SPA cycles increased. The on-state resistance showsessentially no deviation after 1.1 Million SPA. This asymmetricelectrode touchscreen demonstrates the significant robustness andoperability conferred by using the instant invention.

Instant Invention 3 Asymmetric Electrode Touch Switch with Keytec ITOand a Multilayer Conductor of Baytron P AG (First or Buried Layer) andSingle Wall Carbon Nanotubes (Exposed Layer)

An asymmetric electrode based touchscreen was constructed using CoatingB from Table I (400 ohm/square Keytec ITO) as one electrode and CoatingF from Table I (First layer 344 mg/m2 Baytron P AG with 8 mg/m² P3 SWCNT2^(nd) layer) as the second electrode. The single point actuationtesting was performed and gave the results indicated in FIGS. 20 and 21below. This asymmetric electrode touchscreen demonstrated a linearincrease in force to actuate to forces upwards of 300 g before failing.The on-state resistance showed minor deviations after 60,000 SPA. Atapproximately 200,000 SPA, this asymmetric electrode touchscreenexceeded an on-state resistance of 12,000 ohms routinely. It isimportant to note that when contrasted with Comparative Example 4, theusage of the asymmetric electrode architecture and correspondingmaterials significantly improved the lifetime of the Keytec ITO for SPAlifetime. The Keytec ITO touchscreen failed very sharply after a lownumber of actuations. The other interesting point is that by using themultilayer conductor of Baytron P AG and SWCNTs with the very thin filmof SWCNT as the exposed layer, the diode behavior as exhibited inComparative Example 5 was not displayed in Instant Invention Example 3thereby making the Keytec ITO and Baytron P AG compatible.

It is surprising and clearly obvious that the instant invention givessignificant improvements in robustness as demonstrated above. The factthat the instant invention can sustain significantly more actuationsthan the comparative example touchscreens without failing (or failinglater) and/or noticeable change in operation is important due to theimproved reliability of the instant invention touchscreen. For instance,as the force to actuate increases for a touchscreen (use a cellphonewith a touchscreen component as example) over time it will beincreasingly difficult to select certain points on the touchscreenwhereas the instant invention clearly would not suffer such problems.Additionally, the one embodiment of the instant invention eliminated thediode behavior exhibited by ITO and Baytron P AG thereby making thosematerials useful in combination. It is apparent that the exemplaryembodiment can provide drastically enhanced conductor and/or electroderobustness.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

Parts List

-   10 prior art resistive-type touchscreen-   12 device side transparent substrate-   14 first conductive layer, device side-   15 device side first electrode-   16 touch side electrode-   17 touch side transparent support-   18 second conductive layer, touch side-   20 dielectric spacer element-   39 resistive-type touchscreen of the invention-   24 device side exposed electrically conductive layer of the    invention-   25 device side electrode of the invention-   26 touch side electrode of the invention-   27 touch side electrode insulating substrate of the invention-   28 touch side exposed electrically conductive layer-   29 device side electrode insulating substrate of the invention-   32 dielectric spacer element-   59 resistive type touchscreen of the invention-   60 electrode of invention-   62 insulating substrate-   63 insulating substrate-   65 buried electrically conductive layer-   66 exposed electrically conductive layer-   67 exposed electrically conductive layer-   68 dielectric spacers-   70 electrode of invention-   129 resistive touchscreen of the invention-   130 electrode of invention-   132 insulating substrate-   133 insulating substrate-   134 buried electrically conductive layer-   135 buried electrically conductive layer-   136 exposed electrically conductive layer-   137 exposed electrically conductive layer-   138 dielectric spacers-   140 electrode of invention-   100 resistive touchscreen of the invention-   110 touch side electrode-   120 device side electrode-   30 dielectric spacers-   141 touch side bus bar-   142 touch side bus bar-   143 touch side connector electrode-   144 touch side connector electrode-   145 touch side wiring pattern-   146 touch side wiring pattern-   251 device side bus bars-   252 device side bus bar-   253 device side connector electrode-   254 device side connector electrode-   255 device side wiring pattern-   256 device side wiring pattern-   40 bonding adhesive-   301 microscope slide-   302 bottom device side electrode-   303 dielectric spacer dots-   304 copper foil tape-   305 double sided adhesive tape-   306 top touch side electrode

1. A touchscreen comprising touch side electrode and device sideelectrode wherein each electrode comprises an insulating substrate andan exposed electrically conductive layer, wherein said exposedelectrically conductive layers are adjacent and separated by dielectricspacers, and wherein only one of the exposed electrically conductivelayers comprises carbon nanotubes.
 2. The touchscreen of claim 1 whereinat least one of said electrodes comprises an electrically conductivelayer comprising at least one material selected from the groupconsisting of electronically conductive polymers, transparent conductingoxides and transparent metal films.
 3. The touchscreen of claim 2wherein said electrically conductive layer comprises a mixture of acationic polyethylenedioxythiophene and polyanion.
 4. The touchscreen ofclaim 2 wherein said electrically conductive layer comprisespolypyrrole, polyaniline or polythiophene.
 5. The touchscreen of claim 2wherein said electrically conductive layer comprises tin doped indiumoxide, fluorine doped zinc oxide, aluminum doped zinc oxide, indiumdoped zinc oxide, antimony doped tin oxide, or fluorine doped tin oxide.6. The touchscreen of claim 2 wherein said electrically conductive layercomprises a transparent metal film comprising silver, gold, copper,palladium, platinum or alloys of these materials.
 7. The touchscreen ofclaim 1 wherein said carbon nanotubes comprise single wall carbonnanotubes.
 8. The touchscreen of claim 1 wherein said carbon nanotubescomprise covalently attached hydrophilic species
 9. The touchscreen ofclaim 8 wherein the hydrophilic species is present in an amount ofbetween 0.5 and 5 atomic %.
 10. The touchscreen of claim 8 wherein saidhydrophilic species comprises carboxylic acid or carboxylic acid salt ormixtures thereof.
 11. The touchscreen of claim 8 wherein saidhydrophilic species comprises a sulfur containing group selected from:SO_(x)Z_(y) Wherein x may range from 1-3 and Z may be a Hydrogen atom ora metal cation selected from the metals Na, Mg, K, Ca, Zn, Mn, Ag, Au,Pd, Pt, Fe, Co and y may range from 0 or
 1. 12. The touchscreen of claim8 wherein said carbon nanotubes have an outer diameter of between 0.5and 5 nanometers.
 13. The touchscreen of claim 8 wherein said carbonnanotubes comprise bundles of a diameter of between 1 and 50 nanometers.14. The touchscreen of claim 8 wherein said carbon nanotubes comprisebundles of a diameter of between 1 and 20 nanometers.
 15. Thetouchscreen of claim 8 wherein said carbon nanotubes have a length ofbetween 20 nanometers and 50 microns.
 16. The touchscreen of claim 8wherein said carbon nanotubes comprise bundles of a length of between 20nanometers and 50 microns.
 17. The touchscreen of claim 8 wherein saidcarbon nanotubes are metallic carbon nanotubes.
 18. The touchscreen ofclaim 8 wherein said hydrophilic species comprises sulfonic acids orsulfonic acid salts or mixtures thereof.
 19. The touchscreen of claim 1wherein said carbon nanotubes are open end carbon nanotubes.
 20. Thetouchscreen of claim 8 wherein said covalently attached hydrophilicspecies is present on the outside wall of said carbon nanotube.
 21. Thetouchscreen of claim 1 wherein the electronically conductive layercomprising carbon nanotubes further comprises a binder.
 22. Thetouchscreen of claim 1 wherein at least one of said electrodes furthercomprises an electronically conductive layer adjacent the substratehaving a sheet resistance of between 10 and 10,000 Ohm per square. 23.The touchscreen of claim 1 wherein said electronically conductive layercomprising carbon nanotubes have a sheet resistance of between 10² to10⁶ Ohm per square.
 24. The touchscreen of claim 2 wherein saidelectronically conductive polymer comprises a binder.
 25. Thetouchscreen of claim 24 wherein said binder comprises polyvinylalcohol,polyvinylbutyral, polyacrylates, polyurethanes or epoxies.
 26. Thetouchscreen of claim 1 wherein said screen is capable of greater than500,000 single point actuations.
 27. The touchscreen of claim 1 whereinsaid touchscreen has a visible light transparency of greater than 70percent.
 28. The touchscreen of claim 1 wherein said substrates have avisible light transparency of greater than 70 percent and comprisepolyethyleneterephthalate, polyethylenenaphthalate, polycarbonate orglass.
 29. The touchscreen of claim 1 wherein said touch side substratefurther comprises an anti-glare coat.
 30. The touchscreen of claim 1wherein said touch side substrate further comprises an anti-reflectioncoat.
 31. The touchscreen of claim 1 wherein said touch side substratefurther comprises a hard coat having a pencil hardness greater than 2H.32. The touchscreen of claim 1 wherein said touch side substrate furthercomprises a ultra violet light absorbing layer.
 33. The touchscreen ofclaim 1 wherein the force required to actuate a point on the touchscreendoes not change by more than 50 percent over 500,000 single pointactuations.
 34. The touchscreen of claim 1 wherein said the exposedlayer comprising carbon nanotubes further comprises electricallyconductive polymer, metal particles, or transparent conducting oxideparticles.
 35. The touchscreen of claim 1 wherein the electrode thatdoes not comprise carbon nanotubes comprises a mixture of electricallyconductive polymer, metal particles, or transparent conducting oxideparticles.
 36. The touchscreen of claim 3 wherein said mixture of acationic polyethylenedioxythiophene and polyanion has a figure of meritof less than
 50. 37. The touchscreen of claim 1 wherein said exposedlayer comprising carbon nanotubes is on the touch side of saidtouchscreen.
 38. A device comprising a display device having attachedthereto a touchscreen comprising touch side electrode and device sideelectrode wherein each electrode comprises an insulating substrate andan exposed electrically conductive layer, wherein said exposedelectrically conductive layers are adjacent and separated by dielectricspacers, and wherein only one of the exposed electrically conductivelayers comprises carbon nanotubes.
 39. The device of claim 38 whereinsaid display device comprises a LCD based display.
 40. The device ofclaim 39 wherein said LCD comprises a polarizer plate and thetouchscreen is adhesively attached to said polarizer plate.